1. Field of the Invention
The present invention relates to a magnetron for a microwave oven, and more particularly to an antenna feeder fixing device for such a magnetron.
2. Description of the Prior Art
Referring to FIG. 1, there is illustrated an example of a conventional magnetron for a microwave oven. FIG. 2 is a sectional view of a vacuum body of the magnetron shown in FIG. 1. As shown in FIGS. 1 and 2, the magnetron comprises a hollow cathode shield body 1 and a filament 2 disposed in the cathode shield body 1 and adapted to emit thermions. The cathode shield body 1 is disposed in a hollow magnetron body constituted by an upper member 5 of a plate shape and a lower member 6 of a cylindrical shape. The cathode shield body 1 also has upper and lower portions protruded beyond upper and lower members 5 and 6, respectively. To seal and support the cathode shield body 1, an A-seal member 3 and an F-seal member 4 are provided at the upper and lower portions of the cathode shield body 1. Around the filament 2, a plurality of vanes 7 are placed to receive microwave energy generated when the thermions emitted from the filament 2 are acceleratively rotated in an interaction spacer 9 which is defined between the wall of the cathode shield body i and the filament 2. The magnetron also comprises an antenna feeder 8 adapted as a microwave transfer path for guiding microwave energy received by the vanes 7 into a cooking chamber of the microwave oven. The antenna feeder 8 is supported to the upper member 5 of magnetron body by the A-seal member 3. In the magnetron body, upper and lower permanent magnets 10 and 10' are attached to upper and lower members 5 and 8, respectively, to generate a magnetic field. The magnetic field is transferred to the interaction space 9, by means of pole pieces 11 and 11'. Around the cathode shield body 1, a plurality of cooling fins 12 are disposed which function to release outwardly heat generated in the interaction space 9 and thus cool the interior of cathode shield body 1. Strap rings are also provided for adjusting frequencies of the thermions rotating acceleratively in the interaction space 9. The strap rings are fitted in strap grooves 25 formed at a desired portion of each vane 7. A center lead 17 and a side lead 18 are supported to the lower member 6 of magnetron body by means of the F-seal member 4 and extend downwardly beyond the cathode shield body 1. The central lead 17 and side lead 18 are connected at their one ends to both ends of the filament 2, respectively, so as to apply electric power to the filament 2. A choke coil 15 is also provided to remove conductive noise generated by lead current. To the other ends of leads 17 and 18, a through type condenser 14 is connected, which functions as a terminal making it possible to apply easily electric power from the external to the filament 2. The condenser 14 cooperates with the chock coil 15 to enhance a shield effect on conductive noise. Beneath the housing, a filter box 13 is disposed to surround the lower portion of the cathode shield body 1. The filter box 13 functions to remove radiation noise emitting through both the center lead 17 and the side lead 18.
In this conventional magnetron with the above-mentioned construction, a magnetic circuit is formed along the upper member 5, the lower member 8 and the pole pieces 11 and 11', by the electric field of permanent magnets 10 and 10' so that a magnetic field is generated in the interaction space 9. Under this condition, as electric power is applied to the filament 2 via the center lead 17 and the side lead 18, an electric field is generated between the filament 2 as a cathode and the vanes 7 as an anode, thereby causing the filament 2 to emit thermions which are, in turn, radiated into the interaction space 9. In the interaction space 9, the thermions conduct a cycloidal movement, that is, an accelerated rotation, by axial magnetic fluxes generated from the pole pieces 11 and 11' and an electric field generated between the filament 2 and the vanes 7. On the other hand, microwave energy transmitted to the vanes 7 is fed into the cooking chamber, via the antenna feeder 8 and a waveguide (not shown) of the oven, thereby heating the food placed in the cooking chamber.
On the other hand, it has been known that in the above-mentioned magnetron, the distance between the antenna feeder 8 and the wall of cathode shield body 1 is one of factors causing a variation in output of the magnetron. In this regard, various magnetrons having different outputs have been conventionally provided by varying the distance between the antenna feeder 8 and the wall of cathode shield body 1 according to the model of magnetron.
FIG. 3 is a plan view showing the cathode shield body and vanes of the conventional magnetron. On the other hand, FIG. 4 is a perspective view of the vanes of the conventional magnetron. As shown in FIGS. 3 and 4, a plurality of vanes 7 are formed to extend radially toward the central axis of the cathod shield body 1. Every other vane 7 has at its upper surface a groove 16 for engaging with the antenna feeder 8. Each vane 7 also has stepped strap grooves 25 at its upper and lower surfaces, respectively. In the stepped strap grooves 25, strap rings are fitted, respectively.
Each groove 16 is spaced apart from the inner wall surface of cathode shield body 1 by a constant distance d. As a result, the antenna feeder 8 which is engaged with the groove 16 is also spaced apart from the inner wall surface of cathode shield body 1 by the constant distance d.
It is known that the output of magnetron is increased upon an increase in the distance d and decreased upon a decrease in the distance d.
In the above-mentioned construction, however, there is a disadvantage that the distance d between the antenna feeder and the inner wall surface of cathode shield body 1 is always constant, because only one groove 16 is provided at the upper surface of every other vane 7 of the cathode shield body 1. As a result, this type of vanes 7 can not be applied to other models of magnetrons having different outputs.
That is, where a magnetron having a different output is desired to be manufactured, there is a requirement of a different type of vanes having different groove position. This causes a difficulty in using modular elements for providing various models of magnetrons. As a result, it is required to prepare various molds for forming respective vanes for various magnetron models, thereby causing the manufacture cost to increase.